The present disclosure relates to a head-mounted display mounted on the head of the user to provide a virtual image and, more particularly, to a head-mounted display that provides a virtual image letting the user experience the same realism as in the best seat in a movie theater.
A 3D image which can be stereoscopically viewed can be provided for an observer by displaying images having parallax on right and left eyes of the observer. It has been expected that a 3D image technique is applied to various fields such as television broadcast, films, telecommunication, and telemedicine. For example, a time-division stereoscopic image display system that has a combination of a display device and 3D eyeglasses has already been widespread (For example, refer to Japanese Unexamined Patent Application Publication No. 2010-21731). The display device alternately displays a left-eye image and a right-eye image that have parallax on a screen in a particularly short cycle. The 3D eyeglasses have shutter mechanisms which are liquid crystal lenses, for example, and provided for a left-eye part and a right-eye part respectively.
A display device that the user wears on his or her head to see a video image, namely, a head-mounted display (HMD) has been widespread. A head-mounted display includes a display device for each of left and right eyes and is used with a headphone so that senses of sight and hearing can be controlled. If the head-mounted display is configured so as to completely block external environments when it is mounted on a head, a sense of virtual reality in watching is increased. The head-mounted display can project different video images to left and right eyes. If images having parallax are displayed on left and right eyes, a 3D image can be provided in the same way as above.
A head-mounted display is a display system that provides the user with a virtual image (that is, a virtual image is focused on the retina). When an object is present in a position closer to the lens than the focal point, a virtual image appears on the object side.
When the user sees a virtual image, it is preferable, for example, to change the distance between the user and the point where a virtual image is formed, depending on the video image. For example, a display device that provides a virtual image appropriate for the video image is proposed (see Japanese Unexamined Patent Application Publication No. 2007-133415, for example). This display device has a magnifying optical system that places the same virtual image observed by the left and right eyes of the user on a single plane, and controls the distance between the user and the virtual image and the magnification of the virtual image depending on the aspect ratio of the video image. For example, for the video image of a movie or drama with a aspect ratio of 16 to 9 based on high definition broadcast, a large virtual image at a far position approximately 15 meters away from the user is focused on the retina. For the video image including television signals with a aspect ratio of 4 to 3 based on the NTSC (National Television System Committee) system, a middle virtual image at a relatively close position approximately 3 meters from the user is focused on the retina to let the user experience realism and reduce tiredness during seeing of the virtual image.
If a device with high resolution such as organic electro-luminescence (EL) is used as the display units of the left and right eyes of the head-mounted display, an adequate field angle is set by an optical system, and multichannel is reproduced by the headphone, then the same realism as in the best seat in a movie theater can be reproduced. The inventors are going to develop a head-mounted display that provides the same audio-visual environment as in the best seat in a movie theater.
In a product of the related art, an approximately 60-inch virtual image approximately several meters away is focused on the retina and the angle of view is a little under 40 degrees. When this situation is thought in terms of a movie theater, a seat several meters away from the screen is not a good seat and this angle of view is not large enough for movie appreciation. On the other hand, if the angle of view is too large, the user should move the face when reading a caption displayed near an end of the screen, so this situation is not appropriate for movie appreciation.